The aim of this proposal is to examine membrane structure by a method that provides information of a type that is currently unavailable anywhere in the membrane literature. Lipids will be synthesized which have C-13 specifically incorporated at two sites along the chains. Long-range carbon-carbon couplings will reveal the details of chain conformation and packing--key to understanding the premeability properties of membranes and the diseases associated with abnormalities in these properties. The method has many advantages: (a) Interpretation of the data is simple and straightforward. (b) There are no potentially perturbing "probes". (c) Both ordered and disordered systems may be examined. (d) The information is specific, not "global", in the sense that trans-gauche populations are provided at known locations along the chains as opposed to "total populations over the entire chain". (e) The method may be applied to a host of other biologically and medically important systems including binding to enzymes, antibodies, and receptor sites. Initial results with micellar and enzymatic association demonstrate the power and workability of the method.